1. Field of the Invention
The present invention relates to cellular telephone signal transmission and more particularly to circulators and isolators used in the transmission of high-frequency signals such as cellular telephone signals.
2. Description of the Prior Art
Cellular telephone service is becoming exceedingly popular and is very much in demand. Cellular telephones operate in a frequency band considerably higher than the normal AM/FM radio and use circulator/isolator devices for preventing intermodulation and appropriately directing the signal in the transmitting circuit. A circulator is an isolator without a load attached thereto.
In the assembly of circulator/isolator devices, the garnet(s), center conductor, pole piece and magnets have been held together by four different methods. The first method has the magnets and pole piece held together by a wrap of a copper or similar material or with a separate magnet casing, and the garnet or garnets held to the center conductor with an adhesive. In the second method, the magnets are held together as in the first method but the garnet or garnets are held to the center conductor with a dielectric grease. The third method employs adhesive to hold together the magnets, pole piece, garnet or garnets and center conductor. The fourth method includes all aforementioned components being held together with a dielectric grease. In all four methods, a clamp, whether it be a separate clamp or the housing, is utilized to hold the assembly together under pressure. Such pressure can crack the brittle garnets.
In all of the four above mentioned methods, there is a compound, whether it be adhesive or dielectric grease, which is between the center conductor and garnet or garnets. This compound increases the insertion loss of the circulator/isolator device. Also, during the assembly process, added labor is needed to apply the compounds to the components thereby increasing the cost of the device. In each of the methods, either an extra fixture must be provided to center all of the components with respect to each other or, as in most cases, the centering is "eyeballed" by the person assembling the device. Improper centering tends to decrease the performance of the device.